STUDIES IN HUMANS. The relationship of HLA-B27 to spondyloarthropathic disease will be investigated in a population of HLA-typed subjects, including B27+ and B27- normal controls, B27+ and B27- patients with spondyloarthropathies, control patients with other rheumatic diseases, and selected families. Peripheral blood lymphocytes from these individuals will be subjected to two fundamental lines of experimentation: (1) The cells will be assayed for susceptibility to lysis by a panel of human cytolytic T lymphocyte clones, each specific either for an epitope on the HLA-B27 molecule or for a control antigenic determinant. Correlations will be made within the study population between B-27-associated, cytolytic T cell-defined epitopes and the presence or absence of B27-associated spondyloarthropathic disease. These experiments will test the hypothesis that a T cell-defined HLA determinant is more closely associated with disease susceptibility than is serologically defined HLA-B27. (2) Genomic DNA extracted from the cells will be digested with restriction endonucleases; the resulting DNA fragments will be electrophoretically separated, blotted, and hybridized by the method of Southern with one or more 32P-DNA probes specific for base pair sequences of the HLA-B locus. Correlations will be made within the study population between the observed restriction fragment length polymorphism and the presence or absence of HLA-B27 and/or B27-associated disease. The combination of these two experimental approaches should yield a high probability of determining whether the spondyloarthropathic disease factor is the B27 molecule itself or an allele at a linked locus. B27-specific and/or disease-associated DNA restriction fragments will be cloned and subjected to further characterization. STUDIES IN RATS. The T lymphocytes initiating the pathogenesis of adjuvant arthritis in the rat, an experimental model of seronegative polyarthritis and spondylitis, will be characterized. Lines of arthritogenic T cells will be established in continuous culture from arthritic rats and evaluated for their antigenic reactivity, patterns of trafficking in vivo, and cell surface phenotype. These animal experiments should provide insight into the role of T lymphocytes in the pathogenesis of systemic spondyloarthritis.